As is commonly known, liquid crystal display panels are comprised of arranging opposing glass plates in which liquid crystal is sealed on a liquid crystal drive substrate that applies an electric field to the liquid crystal. This liquid crystal display panel regulates the electrical field applied to the liquid crystal by controlling the data voltage applied pixel electrodes of the liquid crystal drive substrate, and displays images by controlling the optical transmittance of the liquid crystal by this regulation of the electric field.
Liquid crystal drive substrates for such liquid crystal display panels are provided with a plurality of pixel electrodes arranged in the form of a matrix on a glass substrate, and together with supplying a data voltage to these plurality of pixel electrodes by the data lines, are composed so that, together with providing TFT and other switching elements between the data lines and pixel electrodes, the TFT elements are controlled according to a gate voltage supplied by the gate lines. Namely, writing of the data voltage to the pixel electrodes is controlled by the data voltage supplied to the TFT by the data lines, and the gate voltage supplied to the TFT by the gate lines. By arranging liquid crystal drive substrates composed in this manner in opposition and in close proximity to each other on a liquid crystal plate, the electrical field resulting from the voltage that is substantially applied to and held in the pixel electrodes (pixel voltage) acts on the liquid crystal resulting in the display of images on the surface of the liquid crystal plate.
For example, the electro-optical element plate (referred to as a modulator) described in Japanese Unexamined Patent Application, First Publication No. Hei 5-256794 is used as an inspection apparatus that inspects the operation of such liquid crystal drive substrates. This inspection apparatus is comprised of arranging opposing modulators on a liquid crystal drive substrate serving as the inspection target, and in the case of applying a prescribed data voltage to each pixel electrode of the liquid crystal drive substrate, capturing different modulator images corresponding to the status of voltage applied to the pixel electrodes (voltage image) by an image capturing means such as a CCD camera, and calculating the voltage of each pixel electrode based on the electro-optical characteristics of a modulator for which this voltage image has been preconfirmed (pixel voltage) to judge whether or not data voltage is normally applied to each pixel electrode, namely to judge the quality of the liquid crystal drive substrate corresponding to the manner in which defective pixel electrodes to which data voltage is not normally applied are distributed.
In inspection apparatuses of the prior art that used such a modulator, when pixel voltage is calculated from a voltage image, normal pixels and defective pixels are judged by converting to binary by comparing the pixel voltage with a prescribed threshold value. In this case, the threshold value of an inspection apparatus of the prior art is used to judge defective pixels by setting a single threshold value, the following problem existed.
FIG. 14 is a characteristics drawing showing the relationship between pixel voltage and threshold value for explaining this problem. In this drawing, the horizontal axis indicates pixels, namely the locations of pixels in the direction in which they are arranged, while the vertical axis indicates the pixel voltage of each pixel in the direction in which they are arranged. Here, the pixel voltage of each pixel demonstrates the pixel voltage or the pattern by which pixel voltage changes corresponding to the type of non-conformity in the case there has been some type of non-conformity in the mechanism by which data voltage is written to the pixels.
For example, examples of types of defective pixels (defect types) include (1) open line defects, (2) point defects and (3) shorted line defects. Open line defects occur as a result of a disconnection at some location in the above data lines or gate lines, and are defects in which data voltage is not normally written to a plurality of consecutive pixel electrodes. As shown in the drawing, the pixel voltage of pixel electrodes having this type of open line defect (open line defect sections) is such that a value considerably lower than the pixel voltage of normal pixels continues across a plurality of pixels.
Point defects refer to defects in which data voltage is not written normally to a single pixel electrode, and occur due to insulation defects of a certain pixel electrode or an operation defect of a TFT provided in the pixel electrode. As shown in the drawing, the pixel voltage of a pixel electrode having this type of point defect (point defect section) is a low value over the range of a single pixel relative to the pixel voltage of normal pixels, and is typically somewhat higher than the above-mentioned open line defect sections.
In addition, shorted line defects occur due to shorting of the above data lines or gate lines at any location, and are defects in which data voltage is not normally written to a plurality of consecutive pixel electrodes. As shown in the drawing, the pixel voltage of pixel electrodes having this type of shorted line defect (shorted line defect sections) is such that a value that is not extremely different from the pixel voltage of normal pixels continues across a plurality of pixels.
In this manner; the pixel voltage obtained from the voltage image of the modulator becomes various values corresponding to the type of defect, and the magnitude of that value for each type of defect is determined statistically through an inspection of the liquid crystal drive substrate. In addition, normal pixels demonstrate variation over a fixed range for pixel voltage according to various causes, and that pixel voltage may be a voltage value that approximates a shorted line defect (normal point) as shown in the drawing.
In inspection apparatuses of the prior art, defective pixels and normal pixels were judged by setting a single threshold value for this type of pixel voltage. This threshold value is determined for each actual production step of the liquid crystal drive substrates based on the extent to which an inspection standard is set and so forth. As shown in the drawing, in the case of setting, for example, a single threshold value, a normal point is judged as a defective pixel. In addition, in the case of setting two threshold values in order to avoid this, it becomes no longer possible to detect shorted line defect sections. Thus, in the case of judging defective pixels and normal pixels by setting a single threshold value as in the prior art, together with it not being possible to accurately classify each type of defect, the accuracy of the judgment of defective pixels itself becomes poor.
On the other hand, in this type of inspection apparatus, improvement of throughput is an extremely important performance element. Efforts have been made in the past to shorten the time required to inspect a single liquid crystal drive substrate, namely to improve throughput, by making contrivances in the inspection algorithm and so forth. Thus, in solving the above problem, it is necessary to pay attention to this point. Although it is possible to achieve improvement of inspection accuracy of the inspection apparatus by solving the above problem, it is necessary to simultaneously ensure that there is no decrease in throughput.
In consideration of the above problems, the objects of the present invention comprise the following:    (1) to improve inspection accuracy of liquid crystal drive substrates;    (2) to judge types of defects more accurately; and,    (3) to improve inspection accuracy of liquid crystal drive substrates without decreasing throughput.